All passwords gone after migration to new Windows installation

I have copied everything from the old profile folder to the new installation:C:\Users\John\AppData\Roaming\Opera Software\Opera Stable\ (new Drive Letter and Username are the same as in the old installation)

But when I open Settings > Privacy & security > Passwords > Show all passwords I get an empty list.
Besides, my passwords are NOT backed up in Opera Sync, because I forgot my password and had to reset my whole Sync Data.
I had about 200 passwords which are now gone.

Passwords are encrypted to your user account (and not just the name), hence they are unusable in a clean install. If you have the old disk there may be some files or just registry keys you could copy to reinstate the old account (I'm not completely certain), otherwise you're stuck with the brute force method you mentioned at the end there.

I would recommend .CSV + KeePass (Or another Pss Manager) + Browser extension then you are able to use your passwords in any browser and device (Desktop, Mobile, Tablet...), (does Opera mini/mobile save passwords? In every platform?).

As said in this post using the "exporter tool", (well ChromePass in this case) you could create a .CSV, then import the file, install the appropriate extension and access your passwords everywhere everytime.

I prefer the freedom to have them secure in a Password Manager and the ability to use them everywhere, without depending on the browser.

Checking the app, you can export them as .csv and as Keepass .csv also, but if you prefer to use just Opera, maybe the ChromePass .Csv could be imported into Opera enabling the Flag.

The method of celadyn did work up to the import of the passwords into ChromePass,
but the passwords did not appear in the settings in opera.

Now i have found an solution:

I used the same Username and password on the new clean windows installation and installed Opera.

Then i copied the whole opera "Program Folder" and the "Profile Folder" from the old onto the new maschine.
(All settings, except the passwords, have been taken over to the new opera)

Type "opera://flags" in Opera addressbar and press Enter. It'll open Opera experiments page.
There you must search for "Password import and export" and activate this flag.
(!! Do this in both opera installations !!!)

In both opera installation will now appear an "export" and an "import" -Button under
Settings > Privacy & security > Passwords > Show all passwords

Now you only have to export the passwords from the old opera by saving them in an CSV-File
and importing the saved CSV-File into the new opera.